Protective coatings on metals



3,007,818 Patented Nov. 7, 1961 3,007,818 PROTECTIVE COATINGS N METALS Kurt Erich Schimkus, Chicago, Ill., assignor to Acme Steel Company, Chicago, 111., a corporation of Illinois No Drawing. Filed Mar. 31, 1958, Ser. No. 724,794 44 Claims. (Cl. 148-616) This invention relates to protective coatings on metals and to coating baths and coating methods for applying the coatings.

Many coatings and coating methods have been utilized heretofore to protect base metals, i.e., metals which corrode and discolor upon exposure to high humidity conditions and to salt water and the like. In certain instances it is desirable that such coatings be transparent whereby to leave substantially unchanged the appearance of the surface coated. In other instances it is desirable to color the metal surface to be coated and, accordingly, the coating must either be colored or readily receive coloring agents.

One specific example of an application in which it is desired to impart a particular color to a metal surface is in the case of galvanized steel strapping. It has been found advantageous to color such steel strapping black. The methods which have heretofore been employed for providing black coatings on strap steel or the like have not been entirely satisfactory. If the steel is painted to provide the desired color and protective coating, it is not possible to provide an even and uniform coating when the metal is moved at high speed during the coating process and small pin holes are often present in the coating with the result that the strip rusts at these bare spots and the rusty solution bleeds out onto the surface of the paint. Another prior method comprises the step of passing a galvanized steel strip through a nickel salt solution which must be maintained at a high temperature, but this method has the disadvantage that the resulting black nickel oxide coating rubs off easily so that it is necessary to provide an additional coating of lacquer to protect it. Also, when this method is carried on with the metal strip moving at high speeds, a uniform coating cannot be insured and there are resulting bare spots where the metal is protected only by the zinc coating provided by the galvanizing process. In general, prior color coatings have had the disadvantage that there has been no chemical union between the coating and the metal base.

Special problems are encountered when the metal part is to be exposed to high temperature and high humidity conditions which may also include salt Water. Such conditions are often encountered in the tropical regions. The protection of metals under such conditions is most difficult. In one practice heretofore a coating of zinc has been provided on steel products as in the usual galvanizing processes. Such zinc coated parts as well as cadmium plated parts and aluminum and zincbase die cast parts have heretofore further been provided with chromate conversion coatings to provide additional protection therefor. Furthermore, these coatings in turn have sometimes been covered with lacquer or paint to improved both the protection and the appearance of the articles.

In the absence of the additional protective coatings set forth above zinc, for example, when exposed to moisture develops a bulky white corrosion deposit. This deposit is particularly troublesome in tropical climates where the daily temperature variations cause an intermittent condensation of moisture in the nature of dew. The storage of zinc coated parts in unheated warehouses or the packaging of them in unseasoned Wood containers or damp paper also causes this type of corrosion deposit which often impairs the operation of certain types of equipment such as relays and switches. The chromate coatings referred to have been employed in an effort to overcome this difiiculty.

It has been the usual practice to apply chromate coatings by an immersion process although electrolytic methods have sometimes been employed. The compositions of these baths are largely made up according to secret formulae but it is known that they all contain two basic ingredients, viz., hexavalent chromium ions and mineral acid with the addition, in some cases, of one or more organic acids. On immersion, the zinc coated or cadmium plated article is attacked by the mineral acid with an attendant rise in the pH of the solution adjacent to the metal. At the same time some hexavalent chromium is reduced to the trivalent state. When the pH reaches a critical value, the trivalent chromium and some hexavalent chromium are deposited on the metal surface.

The chromate films which are thus deposited are generally noncrystalline, nonporous and gel-like. They are quite susceptible to being damaged by abrasion immediately after being formed and should, therefore, be allowed to age from twelve to twenty-four hours before being subjected to normal handling operations in the shop. When the chromate coatings are applied by electrolytic methods these precautions need not be taken.

The chromate films which give maximum protection are those which contain both trivalent and hexavalent chromium. The nonporous nature of the film enables it to exclude moisture from the metal to a very great extent and, if there are any discontinuities in the film, the hexavalent chromium, being slightly soluble, exerts a well known inhibiting action. It has been found that the formation of the undesirable white corrosion product is inhibited as long as there is a small amount of hexavalent chromium in the film.

Although chromate coatings have found. wide industrial use, it appears that, because of the above mentioned liability to abrasion, they have been employed only on parts which are substantially static when. in use as distinguished from moving parts and parts having contact with each other or with other members, such as continuously moving metal strips which are acted upon during their movement by forming or shearing members. Furthermore, chromate coatings cannot be applied by continuous strip processes since the coating being gel-like would be readily removed by the strip feeding mechanism immediately after formation and before it had an opportunity to age.

Accordingly, it is an important object of the present invention to provide improved protective coatings for base metal surfaces and improved coating baths and coating methods to apply the coatings to the base metals.

Another object of the invention is to provide improved coatings for base metals which are substantially colorless and transparent whereby to leave unimpaired the desirable surface characteristics of the base metal while providin g a maximum protection therefor.

Yet another object of the invention is to provide coating methods and baths which can apply protective coatings of the type set forth to the surfaces of coating metals such as zinc with substantially less depletion of the zinc as compared with prior coating methods and baths.

Still another object of the invention is to provide protective coatings of the type set forth which are more readily colored to provide pleasing and durable colored protective coatings.

In connection with the foregoing object it is another object of the invention to provide improved coating methods in which a colored protective coating can be produced on a base metal surface in a single step process.

Yet another object of the invention is to provide a proved coatings formed of a combination of protective compounds and coating methods which can deposit these combinations of protective compounds simultaneously in a one step process.

Yet another object of the invention is to provide a galvanized steel strip having a black coating which is chemically united with the zinc and thereby tightly bonded thereto, the color coating being uniformly and evenly distributed so that there are no bare spots and no additional protective coating is required.

Still another object of the invention is to provide an improved method of applying a black coating to base metal surfaces in which the coating is effected by immersing the base metal in a coating solution at room temperature, thereby avoiding the necessity of providing the expensive heating equipment which has been required when coating with prior compounds such as nickel salts and the like.

It has now been found that good protective coatings can be applied to base metal surfaces by applying thereto a composition containing an anion of a phosphoric acid ester of cyclohexanol distributed in a suitable carrier. A preferred class of materials is the anion of a phosphoric ester of hexahydroxycyclohexane (inositol), the preferred material being the anion of inositol hexaphosphoric acid commonly called phytic acid. It also has been found that these compounds may be applied as the free acid or as a salt thereof, the sodium, potassium, calcium and magnesium salts being particularly advantageous.

A preferred class of carriers useful in the present invention are hydrophilic carriers. For example aqueous solutions, oil-water emulsions and wax-like compositions containing water and other hydrophilic materials can be used satisfactorily. In general any base metal which will react with an acid medium or with a basic medium can be treated successfully to provide a protective coating thereon using this invention. When the coating composition is of an acid character, the pH may be from about 0.8 to about 6.0. Substantially all materials on which the present invention is useful can be treated with such coating compositions. Certain metals such as zinc, cadmium, aluminum and magnesium can also be successfully treated when the coating composition is basic in character. More particularly such compositions are useful when they have a pH of about 7.5 to about 9.0 or

more.

The concentration of the phytic acid or other related coating material used in the present invention is preferably present in the carrier in a concentration of from about 0.001 mole per liter to about 0.1 mole per liter. When combination coatings such as coatings including chromate are formed, the chromate may have a concentration of from about 0.1 to 1.0 mole per liter of coating composition.

By a proper choice of composition and concentration of ingredients and by proper control of the pH. the time for obtaining a satisfactory coating may be from a fraction of a second up to as much as 30 minutes or an hour or more.

The following specific examples of protective coatings, coating methods and coating compositions illustrate the application of the present invention and it is to be understood that these examples are not intended in any way to limit the scope of the present invention.

Example] A clean strip of mild carbon steel was provided. A coating composition was prepared by adding to water an aqueous solution of phytic acid containing 70% by weight of free phytic acid to provide a concentration in the coating solution of about 0.1% by weight .of phytic acid. A

1 N aqueous solution of sodium hydroxide was added until the pH of the coating solution was about 1.5. The steel strip was then immersed in the coating solution for ten seconds to form a coating thereon. The coated strip was then taken from the solution and any excess coating solution removed. After drying, the coated steel strip was examined and found to have a colorless transparent phytate coating thereon. It was determined that between 35 and 40 mg. per square foot of coating had been formed on the strip. In addition to being colorless the coating exhibited good paint adhesion and provided good protection against humidity and salt water when subjected to standard humidity and salt water corrosion tests. The strip so prepared exhibited better corrosion resistance properties than a like steel strip having to mg. per square foot of protective phosphate coating thereon. The method of Example 1 above has been operated successfully when the concentration of phytic acid in the coating solution is increased to as much as 0.2% by weight. Smaller concentrations of phytic aoidcan also be used but resulted in coatings of less weight per square foot for like exposure times. It further was found that the pH of the coating solution could be varied from approximately 1.2 to approximately 1.7 and still provide satisfactory coatings with the same exposure time.

Example 2 A clean zinc surface was provided. A coating solution was made by adding an aqueous phytic acid solution containing 70% phytic acid by weight to water to provide a concentration therein of 0.1% by weight of phytic acid. Sufficient 1 N sodium hydroxide solution in water was added to provide a pH of 3.6 in the coating solution. The zinc surface was then immersed in the coating solution for ten seconds. Thereafter the zinc surface was removed from the solution and dried. It was found that a zinc phytate coating had been formed on the zinc surface. The coating was substantially colorless, provided good paint adhesion and gave good corrosion protection against humidity and salt water as determined by standard corrosion tests.

It was further found that the coating solution gave satisfactory coatings when the phytic acid concentration therein was increased to 0.2% by weight or more. Satisfactory coatings were also obtained when the pH was adjusted between about 3.5 and 3.8.

Example 3 The coating solution and method described above in Example 2 with respect to a zinc surface was also carried out on a cadmium surface. A protective coating was formed on cadmium which was substantially colorless, had good paint adhesion qualities, and provided excellent protection against corrosion by humidity and salt water.

instead of the free phytic acid disclosed in Examples '1, '2 and 3 above, suitable protective coatings can be formed utilizing salts of phytic acid. The coating solution or bath may utilize a carrier other than water and may be basic instead of acidic in pH. The following is an example of the use of sodium phytate in an oil-water emulsion to provide protective coatings on base metals.

Example 4 A roll forming oil was provided which was an emulsion of oil and water. A solution of sodium phytate in water was formed, the concentration of the sodium phytate being 25% by weight. 15 cc. of the sodium phytate solution were added to one gallon of roll forming oil. The resultant coating composition had a pH of 8.0. Galva nized steel plate was then roll formed utilizing the protective coating solution in the same way that the roll forming oil had been used heretofore. In the roll forming operation, portions of the galvanized steel sheet were folded to angles less than 90 whereby to thin and in certain instances rupture the protective galvanized surface to expose the bare steel therebeneath. The roll forming oil provided a protective coating on both the galvanized surface and on the exposed steel surfaces which protected the roll formed piece from corrosion when exposed to high humidity conditions and salt water. Satisfactory operation was obtained at any pH between about 7.5 and 8.7.

In general any of the base metals that react with acidic or basic mediums or solutions can be coated using the above coating solutions. The coating solution may contain for example from about 0.001 mole per liter of phytate ion (empirical formula C H O P to about 0.003 mole per liter or more. When such concentrations are used in an acid solution, the immersion time will be in the order of ten seconds to provide an adequate protective phytate coating. In general if the concentration of phytate is lowered, the amount of coating laid down during a given unit of time will be less. Conversely, if the concentration of phytate ion is increased, a heavier coating of phytate will be formed on the metal during a given period of time. When utilizing an acid medium or carrier, the amount of coating laid down per unit of time is less if the pH is raised and is greater if the pH is lowered. When utilizing a basic carrier, the amount of coating produced during a given unit of time is less when the pH is lowered and greater when the pH is raised. Those skilled in the art will be able to ascertain satisfactory condit-ions for laying down the desired weight of coating from the above examples.

Often it is desirable to color the coating. It has been found that the phytate coatings laid down as described above are particularly receptive to dyes such as the common organic dyes. Paints and oils also adhere well to the coated surfaces.

In certain instances it is desirable to form the phytate coating and to color the coating in a single process step. This can be readily done in one form of the invention by adding a suitable organic dye to the coating solutions of Examples 1, 2 and 3 above. For example it has been found that alizarine dyes can be conveniently incorporated therein. Suitable results were obtained when 0.02 gm. of alizarine red was added per liter of the coating solution of any of Examples 1, 2 and 3 above. The coatings were uniformly colored using the same coating method described. The colors were deep and were retained in the coatings.

If it is desired to form a black colored phytate coating, it has been found convenient to utilize the following coating solution and procedure.

Example The following ingredients were mixed in the proportions indicated:

G. per liter Copper sulfate (CuSO 3 Phytic acid (C H O (H PO 2 Ferrous ammonium sulfate (Fe(NH (SO 1 Citric acid (C HgOqHzO) 1 Alizarine red 0.2

The metal surface to be coated was immersed in the coating solution for 10 seconds. The resultant coating was continuous, closely adherent and colored deep black. The black color was also adherent.

The proportions set forth above may be varied. However, preferably the molecular ratio between the copper sulfate and the phytic acid should be approximately 1 part of phytic acid to 6 parts of copper sulfate. As a greater proportion of copper sulfate is provided relative to the phytic acid, the coating forms more slowly and is not as adherent as that of the example set forth above. Conversely if the proportion of phytic acid is increased relative to the copper sulfate, there is a gradual loss of coloring. One particularly useful application of the coating solution and method of Example 5 is to apply it to 6 the coating of galvauized'steel strap. 'In such a case it is convenient to apply the coating by running the strap endwise through the coating solution. Preferably the pH is maintained within the range of about 3.7 to about 4.3 to obtain best results.

The copper from the copper sulfate is believed to be deposited on the galvanized steel strip as finely divided particles of metallic copper which have a black color. Such a copper deposit may be effected by the immersion of a galvanized steel strip in an aqueous copper sulfate solution with no other ingredients present but, of course, in the absence of other ingredients, the copper does not adhere to the metal strip and may be readily wiped off. Thus, the copper sulfate provides the strip with the black pigment which is believed to be finely divided copper.

The phytic acid reacts with the zinc of the galvanized strip to produce zinc phytate which adheres to the galvanized surface and provides a protection therefor. This zinc phytate coating does not wipe ofl' and it serves to bond the black copper deposit to the zinc surface. By employing a proper balance in the proportions of phytic acid and copper sulfate, it is possible to produce zinc phytate at a suitable rate so that the copper deposit is entrained on the strip by the zinc phytate so that an even black coating is applied continuously to the moving metal strip and adheres firmly thereto. If there is not a proper balance between the copper sulfate and the phytic acid, a brownish or a greenish-brown color is obtained. It may be that this condition results from a too rapid production of zinc phytate which coats the metal strip quickly and forms a barrier which prevents the penetration to the strip of the copper deposit. On the other hand, if too much copper sulfate is present, the zinc phytate does not form fast enough to bond the resulting larger amount of the copper deposit which coats the strip but prevents adequate contact of the zinc phytate therewith so that there is an insufficient bonding of the copper. When this occurs the color of the coating tends toward that of ordinary red copper provided the galvanizing coating has been sufficiently thin to be removed by the action of the copper sulfate; but, if the zinc coating is so thick that it is not removed by the action of the copper sulfate, the color will remain black but may be readily wiped off due to the lack of adequate bonding because of insufiicient phytic acid.

The addition of ferrous ammonium sulfate to the solution deepens the color of the coating. The alizarine red also serves to deepen the color of the coating and to make it more uniform. It removes streaks and may be termed a color leveler.

Citric acid is added to the solution to act as a buffer and to maintain the pH of the solution constant. In the practice of this method, as in any plating process, the control of the pH is necessary to maintain the desired performance of the bath and the quality of the deposits. The preferred range Within which the pH is maintained, as indicated above, has been determined empirically by adjusting the pH and observing the results.

It has been found that the phytate coating can be formed simultaneously with other coatings on the base metal. For example it is possible to co-deposit a phytate and a chromate coating on a base metal according to the present invention. This can be conveniently done by exposing the base metal to an acid solution containing from about 0.001 to 0.1 mole per liter of phytate ion and about 0.2 to 0.6 mole per liter of chromate ion.

The co-formation of a phytate and chromate coating on a zinc surface such as a galvanized steel surface can be conveniently carried out by running a strip of the metal through a coating bath at a temperature of 75 F., the bath having a phytate concentration of 0.02 mole per liter and having a dichromate concentration of 0.4 mole per liter, the pH of the solution being adjusted to between about 1.8, the strip being in the bath for approximately 7 eight seconds. The following is an example of the manner in which the above proportions can be obtained and a specific example of the manner of carrying out the method of the coating.

Example 6 The following ingredients are added in the amounts indicated to sufficient water to form one gallon of coating solution:

Potassium dichromate (K Cr O pound l Sulfuric acid (H 80 grams 12 acid (C6I'I606(H2PO3)6) d Other sources of chromate ion can be used besides potassium dichromate. For example sodium dichromate, chromic acid, other salts of chromic acid, etc., can be used in place of potassium dichromate. Other acids and particularly mineral acids may be used in the place of the sulfuric acid of the above coating solution.

As an example of the use of the improved process, it was employed in the treatment of steel strip having a width of 2 inches and a thickness of 0.011 inch which was galvanized on both sides to a thickness of 0.00004 inch. This galvanized strip was then run through a bath of the coating solution having a temperature of 75 Fahrenheit. The solution was not heated and the process may be carried on at room temperature. The metal strip was in continuous motion through the bath at a speed of about 8 feet per minute and each portion of the strip was immersed in the bath for a period of approximately 8 seconds.

The determination of the optimum concentration of ingredients for the bath was based upon a study of the operation of the ordinary chromate bath when modified by the addition of phytic acid until the most desirable results were obtained. It was found that the best results were obtained with a pH of about 1.7 to 2.0 which was the range found most desirable when the ordinary chromate solution was used. The sulfuric acid acted along with the phytic acid to produce a sufficient acid concentration to maintain the desired pH.

The result of using, the improved bath of Example 6 is the production of a combination zinc phytate and zinc chromate coating on the galvanized steel with the typical yellow chromate discoloring practically eliminated. The coating also has a relatively high resistance to abrasion as compared to former chromate coatings. Any yellow color in the coating may be diminished by shortening the immersion time which also results in a thinner coating. The yellow coloration of the coating is substantially less than that of a chromate coating alone. The coating furthermore is flat in lustre and exhibits substantially no iridescence.

The application of a chromate coating alone to a galvanized surface results in the removal of a substantial amounts of the zinc coating. For example in a typical commercial chromating operation approximately 0.1 mil of zinc may be removed. A combination phytate-chromate coating made according to Example 6 having superior corrosion resistance'properties superior to the chromate coating will by contrast remove only 0.02. mil of zinc. The so-called zinc depletion is therefore substantially less when using the coating solution of Example 6 than when using a comparable chromate coating bath which would give comparable corrosion protection. Actual humidity and salt water corrosion tests demonstate that the coating of Exhibit 6 has substantially greater resistance to corrosion than does a comparable chromate coating.

The coating made according to Example 6 further has been found to be capable of receiving and retaining dyes whereby to provide colored coatings. The dye can be applied by simply running the coated metal through an aqueous solution of the dye as for example 0.2 gm. per

8 liter of alizarine red in water. The resulting coating is uniform in character and pleasing in appearance.

A further advantage of the phytate-chromate coating made by following Example 6 above is the fact that the coating is firm and hard whereby to be resistant to abrasion immediately after the formation thereof. This contrasts sharply with coatings formed of chromate alone which are generally noncrystalline, nonporous, and gellike. Such coatings are extremely susceptible to damage from abrasion immediately following formation and must be aged 12 to 24 hours before being subjected to normal shop handling.

Example 7 The coating solution and method of Example 6 were applied in an identical manner to cadmium plated steel plates. The coatings formed possessed all of the desirable characteristics above with respect to the similar coatings on zinc in Example 6.

Instead of the potassium dichromate utilized in Example 6 it is possible to use other sources of chromate ion such as sodium dichromate as has been discussed above. Furthermore, it is possible to utilize other acids in place of the sulfuric acid such for example as nitric acid. The following is an example of the manner of forming and using such a coating solution whereby to provide 0.55 mole per liter of dichromate and 0.012 mole per liter of pyh-tate in the coating solution.

Example 8 120 pounds of sodium dichrorn ate were dissolved in 25 gallons of water. To this solution was added 5 gallons of phytic acid (70% free p-hytic acid by weight in water). 10 gallons of nitric acid (70%) were then slowly metered into the solution, the solution being continually stirred and cooled to hold the temperature below 110 F. Thereafter sui'licient water was added to make a total of gallons. This concentrated solution was thereafter diluted with 20 times its volume of water to provide a total of 1,000 gallons of coating solution.

The solution was heated to a temperature of 100 F. and maintained at that temperature :5 F. during the coating operation. The pH was maintained at about 0.9 to about 1.3 during the coating operation. At a pH below 0.9 the zinc depletion will be too great whereby substantially to destroy the zinc coating. As the coating operation proceeds the pH increases and control of the pH can be accomplished by adding nitric acid. Preferably the pH should not be permitted to rise above 113 since the solution becomes buffered above that pH and large quantities of nitric acid are therefore needed to bring the pH down to a suitable operating point. When the zinc concentration in the solution has reached approximately 12 gm. per liter, the solution is no longer'useful to pro- 7 vide a suitable phytate-chromate coating. A galvanized steel strip was then fed into and through the solution at a rate such that it was exposed to the solution for ten seconds; The combination zinc phytate-zinc chromate coating formed possessed all of the desirable characteristics'set forth above with respect to Example 6.

Example 9 The coating solution of Example 8 was applied to a Example 11 A tin plated steel strip was coated using the coating solution and coating method of Example 8. The resultant tin phytate-tin chromate coating was not readily disccrnible by visual inspection. The coating, however, gave good protection against corrosion as determined by humidity and salt water exposure tests.

Other carriers can be used in applying the phytate coating besides the aqueous solutions and the oil-water emulsion illustrated above. A hydrophilic wax-like base or carrier has been successfully used in applying a phytate coating to aluminum metal. The following is a specific example of a suitable coating composition utilizing a hydrophilic wax-like base.

Example 12 The following ingredients were mixed in the proportions indicated:

Gm. Cetyl alcohol 7 Stearyl alcohol 3 White beeswax 4 Petrolatum 27 Glycerine 8 A quantity of the coating solution of Example 8 above was treated to evaporate the major portion of the water therefrom whereby to form a paste. 25 grams of the paste so formed were mixed together with the materials set forth above including the hydrophilic base, the saponifying agent and preservative set forth above. The resulting mixture had a pH in the range 2.5 to 2.8. This coating composition was applied to aluminum by spreading a layer thereof on the aluminum surface to be protected. The coating was left in position for about 30 minutes and then wiped 011?. It was found that an aluminum phytate-almninum chromate coating had been formed on the aluminum surface. The coating was highly resistant to corrosion as determined by humidity and salt water exposure tests.

It has been found that the rate of coating can be increased by rapidly flowing the coating solution about the article to be coated. The following is a specific example of such a method.

Example 13 A coating solution as prepared above in Example 8 was diluted with an equal amount of water. The result-ant coating solution was then pumped rapidly through a chamber 4 inches long through which a galvanized steel strip was passed at a rate of 100 feet per minute. The zinc surface was found to be coated with a zinc phytate-zinc chroma-re coating possessing all of the desirable characteristics set forth above with respect to Example 6. The length of contact of the coating solutionwith the Zinc surface being coated was only a fraction of a second.

In carrying out the above examples the phytic acid used was an aqueous solution containing approximately 70% by weight of phytic acid in a relatively pure state. It has been found, however, that it is not necessary to use substantially pure phytic acid and in fact waste solutions or concentrated waste solutions resulting from the steeping of grains called steep liquor is sufficiently rich in phytic acid to work satisfactorily. These liquors contain about -13% phytic acid by weight. The other 10 impurities found therein also do not interfere with the coating reactions.

The present application is a continuation-in-part of my previously filed patent applications Serial Nos. 619,- 400 and 641,256, respectively filed on October 31, 1956, and February 20, 1957, now abandoned.

Although certain preferred examples of the invention have been given for purposes of illustration, it is to be understood that various changes and modifications can be made therein without departing from the spirit and scope of the invention. Accordingly, the invention is to be limited only as set forth in the following claims.

I claim:

1. A coating composition to provide a protective coating on base metals said composition being a paste comprising about 0.001 to about 0.1 mole per liter of phytate ion dispersed in a wax-like hydrophilic base, said composition having a pH in the range from about 2.5 to about 2.8.

2. A coating composition to provide a protective coating on base metals comprising about 0.001 to about 0.1 mole per liter of phytate ion dispersed in an oil-water emulsion, said composition having a pH in the range from about 7.5 to about 8.7.

3. A coating composition to provide a protective coating on base metals comprising an aqueous solution having a pH in the range from about 0.8 to about 6.0 and containing from about 0.001 to about 0.1 mole per liter of phytate ion and copper sulfate in sufiicient concentration to impart a black color to metal contacted by the solution, the ratio of copper ion to phytate ion in said solution being about 6.

4. A coating composition to provide a protective coating on base metals comprising from about 0.001 to about 0.1 mole per liter of phytate ion and from about 0.1 to about 1.0 mole per liter of a salt of chromic acid dispersed in an acidic carrier, said composition having a pH in the range from about 0.8 to about 6.0.

5. A coating composition to provide a protective coating on base metals comprising from about 0.001 to about 0.1 mole per liter of phytate ion and from about 0.1 to about 1.0 mole per liter of chromate ion dispersed in an acidic carrier, said composition having a pH in the range from about 0.8 to about 6.0

6. A coating composition to provide a protective coating on base metals comprising a wax-like acidic hydrophilic base having a pH in the range from about 0.8 to about 6.0 and containing from about 0.001 to about 0.1 mole per liter of phytate ion and from. about 0.1 to about 1.0 mole per liter of chromate ion.

7. A bath for the coating of metal by immersion, comprising an aqueous solution containing about 0.001 to about 0.1 mole per liter of phytic acid, ferrous ammonium sulfate, copper sulfate, the molar ratio of copper sulfate to phytic acid being about 6, and a bufier to maintain the pH of the bath in the range from about 3.7 to about 4.3.

8. A bath for the coating of metal comprising an aqueous solution of the following ingredients in the following proportions per liter of solution: three grams of copper sulfate, two grams of phytic acid, one gram of ferrous ammonium sulfate, one gram of citric acid and twotenths of a gram of alizarine red.

9. A bath for the coating of metal by immersion consisting essentially of an aqueous solution containing a salt of chromic acid, a mineral acid and phytate ion, said salt of chromic acid being present in an amount equivalent to approximately one pound of potassium dichromate per gallon of solution and said phytate ion being present in an amount equivalent to approximately fifty grams of phytic acid per gallon of solution.

10. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition including from about 0.001 to about 0.1 mole per liter of phytate ion dispersed in an hydrophilic carrier, composition having a pH in the range from about 0.8 to about 9.0.

11. The method of providing a protective coating on base metals comprising immersing the base metal in a coating composition comprising an aqueous solution containing about 0.001 to about 0.1 mole per liter of phytate ion, said composition having a pH in the range from about 0.8 to about 9.0.

12. The method of providing a protective coating on base metals comprising spreading a wax-like hydrophilic base having a pH in the range from about 0.8 to about 9.0 containing from about 0.001 to about 0.1 mole per liter of phytate ion on the base metal, and thereafter removing the excess base.

13. The method of providing a protective coating .on base metals comprising applying to the base metal an oil-water emulsion having a pH in the range from about 0.8 to about 9.0 and containing from about 0.001 to about 0.1 mole per liter of phytate ion.

14. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition including an acidic hydrophilic carrier havin a pH in the range from about 0.8 to about 6.0

and containing from about 0.001 to about 0.1 mole per liter of phytate ion and a coloring agent in sufiicient amount to impart a predetermined color to metal contacted by the carrier.

15. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition including an acidic hydrophilic carrier having a pH in the range from about 0.8 to about 6.0 and containing from about 0.001 to about 0.1 mole per liter of phytate ion and an inorganic pigment in sufficient amount to impart a predetermined color to metal contacted by said carrier.

16. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition including an acidic hydrophilic carrier having a pH in the range from about 0.8 to about 6.0 and containing from about 0.001 to about 0.1 mole per liter of phytate ion and an organic dye in sufiicient amount to impart a predetermined color to metal contacted by said carrier.

17. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition including an acidic hydrophilic carrier having a pH in the range from about 0.8 to about 6.0 and containing from about 0.001 to about 0.1 mole per liter of phytate ion and copper sulfate in sufiicient amount to impart a predetermined black color to metal contacted by said carrier, the molar ratio of copper sulfate to phytate ion being about 6.

18. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition including an acidic hydrophilic carrier having a pH in the range from about 0.8 to- 6.0 and containing from about 0.001 to about 0.1 per liter of phytate ion and from about 0.1 to about 1.0 mole per liter of a salt of chromic acid.

19. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition including an acidic hydrophilic carrier having a pH in the range from about 0.8 to about 6. and containing about 0.001 to about 0.1 mole per liter of phytate ion and from about 0.1 to about 1.0 mole per liter of chromate ion.

20. The method of providing a protective coating on base meta-ls comprising applying to the base metal a coating composition including a wax-like acidic hydrophilic base containing about 0.001 to about 0.1 mole per liter of pyhtate ion and from about 0.1 to about 1.0 mole per liter of chromate ion and having a pH in the range from about 0.8 to about 9.0, and thereafiter removing the excess of said coating composition.

21. The method ct coating a galvanized steel strip 12 which consists in immersing the strip in an aqueous solution containing copper sulfate, phytic acid, and ferrous ammonium sulfate, said copper sulfate being present in a concentration of about three grams per liter of solution and said phytic acid being present in a concentration of about two grams per liter of solution.

22. The method of coating a galvanized steel strip which consists in immersing the strip in an aqueous solution containing copper sulfate, phytic acid, ferrous ammonium sulfate, and citric acid, said copper sulfate being present in a concentration of about three grams per liter of solution and said phytic acid being present in a concentration of about two grams per liter of solution.

23. The method of coating a galvanized steel strip which consists in immersing the strip in an aqueous solution of the following ingredients in the following amounts: three grams of copper sulfate, two grams of phytic acid, one gram of ferrous ammonium sulfate, one gram of citric acid and two-tenths of a gram of alizarine red.

24. The method of coating a galvanized or cadmium plated steel strip which consists in immersing the strip in an acidic aqueous solution having a pH in the range from about 0.8 to about 6.0 and containing from about 0.1 to about 1.0 mole per liter of a salt of chromic acid, a mineral acid, and from about 0.001 to about 0.1 mole per liter of phytate ion.

25. The method of coating a galvanized or cadmium plated steel strip which consists in immersing the strip in an aqueous solution having a pH in the range from about 0.8 to about 6.0 and containing from about 0.1 to about 1.0 mole per liter of potassium dichromate, sulfuric acid, and from about 0.001 to about 0.1 mole per liter of phytic acid.

26. A base metal having a protective coating thereon comprising a phytate compound of the base metal.

27. A base metal having a protective coating thereon comprising a phytate compound of the base metal and a coloring agent sufficient to impart a predetermined color to the metal.

28. A base metal having a protective coating thereon comprising a phytate compound of the base metal and black colloidal displacement copper dispersed in said coating.

29. A copper containing base metal having a protective coating thereon comprising copper phytate.

30. An iron containing base metal having a protective coating thereon comprising iron phytate.

31. A zinc containing base metal having a protective coating thereon comprising zinc phytate.

32. An aluminum containing base metal having a protective coating thereon comprising aluminum phytate.

33. A tin containing base metal having a protective coating thereon comprising tin phytate.

34. A base metal having a protective coating thereon comprising a phytate compound of the base metal and a compound of the base metal with an anion consisting of chromium and oxygen.

35. A base metal having a protective coating thereon comprising a phytate compound of the base'metal and a chromate compound of thebase metal.

36. A zinc containing metal member having a coating comprising zinc chromate and zinc phytate.

37. A cadmium containing metal member having a coating comprising cadmium chromate and cadmium phytate.

38. A copper containing metal member having a coating thereon comprising copper chromate and copper phytate.

39. An aluminum containing metal member having a coating thereon comprising aluminum chromate and aluminum phytate.

40. A tin containing metal member having a coating thereon comprising tin chromate and tin phytate.

41. A composition for use in providing a protective coating on base metals comprising essentially a mixture of a first compound selected from the class consisting of phytic acid and salts thereof and a second compound, said second compound being a copper salt, the molar ratio of said second compound to said first compound being about 6.

42. A base metal containing a metal selected from the group consisting of copper, iron, zinc, cadmium, aluminum, and tin and having a protective coating thereon comprising a phytate of the metal selected.

43. A composition for use in providing a protective coating on base metals comprising essentially a mixture of a first compound selected from the class consisting of phytic acid and salts thereof and a second compound from the class consisting of chromic acid and salts thereof, said first and second compounds being present in amounts equivalent to from about 0.001 to about 0.1 mole of the first compound and from about 0.2 to about 0.6 mole of the second compound.

44. A composition for use in providing a protective coating on base metals comprising essentially a mixture of a first compound selected from the class consisting of phytic acid and salts thereof and a second compound from the class consisting of dichromic acid and salts thereof, said first and second compounds being present in amounts equivalent to from about 0.001 to about 0.1 mole of the first compound and from about 0.2 to about 0.6 mole of the second compound.

References Cited in the file of this patent UNITED STATES PATENTS 2,138,295 Fenwicke Nov. 29, 1938 2,250,472 Delong July 29, 1941 2,313,276 Schopmeyer Mar. 9, 1943 2,482,728 Delong Sept. 20, 1949 2,691,035 Calip Oct. 5, 1954 2,750,400 Cowan et al June 12, 1956 2,815,360 Baldwin et al Dec. 3, 1957 2,846,343 Mason Aug. 5, 1958 Patent N00 ,3 OO7,8l8 November 7 i961 Kurt Erich Schirnkus It is hereby certified that error ap ent requiring correction and that the sai corrected below.

pears in the above numbered patd Letters Patent should read as Column 11 line 56 after ;"to" insert about 5 line 57, after O.,l" insert mole a Signed and sealed this 10th day of April 1962,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A COATING COMPOSITION TO PROVIDE A PROTECTIVE COATING ON BASE METALS SAID COMPOSITION BEING A PASTE COMPRISING ABOUT 0.001 TO ABOUT 0.1 MOLE PER LITER OF PHYTATE ION DISPERSED IN A WAX-LIKE HYDROPHILIC BASE, SAID COMPOSITION HAVING A PH IN THE RANGE FROM ABOUT 2.5 TO ABOUT 2.8. 